EFFECTS OF ORANGE JUICE pH ON SURVIVAL, UREASE ACTIVITY AND DNA PROFILES OF YERSINIA ENTEROCOLITICA AND YERSINIA PSEUDOTUBERCULOSIS STORED AT 4C

The objective of this study was to determine the survival, growth rate and possible cellular adaptation mechanisms of Yersinia pseudotuberculosis and Yersinia enterocolitica in orange juice under different pH conditions. Yersinia was inoculated in orange juice with adjusted pH levels of 3.9, 4.0 and 7.0 and stored at 4C for 3, 24, 72 and 168 h. The inter-and intraspecies variation is significant to the pH and time of incubation variables (P < 0.05). At 3.9 pH the cfu (colony forming units) count decreased significantly. At pH 3.9 and 4.0, Y. enterocolitica and Y. pseudotuberculosis survived for at least 30 and 15 days, respectively. Yersinia that survived under low pH in orange juice revealed enhanced urease activity within 12 h of incubation. The attachment gene (ail) could not be detected by polymerase chain reaction in Y. enterocolitica from undiluted sample incubated for 24 h or longer. Moreover, the FesI-restriction profile was altered when Y. pseudotuberculosis was stored at pH 4.0 orange juice for 7 days. These results indicate that Yersinia could survive and grow at low pH and the survival mechanisms could also enable the bacteria to survive the stomach pH barrier to cause enteric infection. PRACTICAL APPLICATIONS The threat of contamination in the nation's food supplies has become an alarming issue. Yersinia pseudotuberculosis and Yersinia enterocolitica are known for their ability to grow at low temperatures and contaminate food supplies. Yersinia spp. were isolated and reported in different food matrices; however the risk of contamination was not sufficiently addressed in orange juice. The focus and application of our study was to investigate the ability of Y. pseudotuberculosis and Y. enterocolitica to survive and grow in orange juice at low pH and incubated at standard storage temperature (4C). There is a Knowledge gap to explain what contribute to the survival and propagation of Yersinia in orange juice. Because of their similar evolutionary origin, the results extracted about Y. pseudotuberculosis will provide valuable information for Y. pestis. Survival in acidic environments is important for successful infection of gastrointestinal pathogens. Therefore, these findings could explain the mechanisms that facilitate Yersinia to tolerate the low pH in the stomach and establish infection.